1. Field of the Invention
The present invention relates to a cylindrical secondary battery, and more particularly, to a cylindrical secondary battery having a center pin capable of improved exhaustion of heat and gas resulting in improved safety by preventing combustion and explosion.
2. Description of the Related Art
Generally, as handheld wireless devices including video cameras, mobile phones and notebook computers are getting compact and multi-functionalized, research on secondary batteries used as a driving power source for these devices is being conducted.
Secondary batteries can be embodied as a nickel-cadmium (Ni—Cd) battery, a nickel-metal hydride (Ni-MH) battery, a nickel-zinc (Ni—Zn) battery, or a lithium (Li) secondary battery. Among them, the Li secondary battery is rechargeable and compact, has a high capacity, a high operating voltage and a high energy density per unit weight, resulting in it being widely used in high technology electronic devices.
The secondary batteries can be classified into cylindrical, prismatic and pouch types depending on the shape of a battery case. Here, cylindrical or prismatic type includes an electrode assembly arranged in a cylindrical or prismatic metal can, and the pouch type includes an electrode assembly arranged in a pouch-type case made out of an aluminum-laminated sheet.
In addition, the electrode assembly in the battery case is a rechargeable power-generating device arranged in a stacked structure of a positive electrode, a separator and a negative electrode. The electrode assembly is classified into a jelly-roll type in which a separator is interposed between a positive electrode and a negative electrode, which are formed in long sheets on which an active material is applied, and a stack type in which a plurality of positive and negative electrodes having a predetermined size are sequentially stacked at opposite sides of a separator. The jelly-roll type electrode assembly is easily manufactured and has a high energy density per unit weight, and thus is mainly used in cylindrical and prismatic batteries.
The cylindrical Li secondary battery includes an electrode assembly wound in a cylindrical shape, a cylindrical can housing the electrode assembly, an electrolyte to allow ions to move, and a cap assembly connected to one side of the cylindrical can to prevent leakage of the electrolyte and prevent separation of the electrode assembly from the can.
Meanwhile, during overcharge or overcurrent, the secondary batteries increase in inner temperature, thereby generating gas. The gas flows toward the cap assembly through a core of the wound electrode assembly and a center pin arranged in the core prevents deformation of the electrode assembly during the charging and discharging of the battery.
A safety vent of the cap assembly is deformed due to the flowing gas, and a circuit in the battery is broken due to the safety vent, thereby preventing the combustion and explosion of the secondary battery.
However, in recent times, as the number of windings in the electrode assembly increases to enlarge the capacity of the cylindrical secondary battery, the diameter of the center of the electrode assembly is reduced.
Accordingly, when the cylindrical secondary battery is combusted, the electrode assembly is deformed due to heat. Through the narrow core, heat and gas generated in the secondary battery find it difficult to be exhausted, resulting in deterioration of safety and reliability of the secondary battery.